Well, I haven't seen Descendants (just some clips here and there on Youtube) so I'm not fully sure what Mal is capable of, but I know she weilds dark magic like her mother. Lily has no dark magic but can turn into a dragon.

While I believe that magic could allow Mal to win, Lily has a greater advantage being a dragon. She has greater strength and the power of flight, which Mal doesn't have (as far as I know). Lily could potentially kill Mal just from squishing her/burning her with her fire breath if Mal wasn't paying attention.

However depending on the circumstances, if Lily is somehow prevented from transforming, Mal wins hands down, as Lily has no magic.

Maleficent is seen transforming in Descendants, but Mal has yet to turn into a dragon so it is unknown if she even can. It is also never stated if Maleficent is a fairy In Descendants; she could just very well be a human with magic in that universe, in turn making Mal human as well. We wouldn't know her full heritage until they tell us who Mal's father is.

Not really. Mal can't turn into a dragon from what I've seen, so their capabilities are different.

Well in generalization, Lily and Mal were probably created around the same time, so they would be based on each other. They're actually quite similar, aside from the fact that Lily is more powerful than Mal. For both Lily and Mal, their father is unknown.They also have similar personalities. So to sum it up, Mal and Lily would be one person rather than two different ideas.

Mal Bertha wrote:Mal will win the fight. Why? 1, She can turn into a dragon (Source:Descendants 2). 2, She can do magic (Source: Also from Descendants 1 and 2).

Lily, however, can only turn into a dragon, not do any magic.

So, the winner is:
Mal

1- I think Mal wouldn't even have to turn into a dragon to win - she has a spell that allows her to levitate, and presumably there is a spell in there somewhere that grants fire manipulation or fire resistance.